In the continuous casting of steel bodies it is known to utilize continuous casting molds which may be curved, as described at pages 707 ff. of the Making, Shaping and Treating of Steel, published by the United States Steel Company, Pittsburgh, Pa., Ninth Edition, 1971.
Molds of this type are filled from above with molten metal, generally by a tundish and/or ladle, the molten steel solidifying in the mold into a continuously-cast ingot.
To reduce the imperfections which appear in the ingot, a continuous casting mold may be associated with an inductor which is energized with alternating current to induce an alternating magnetic field within the mold in the region in which the metal is still molten. This magnetic field, in turn, propels the molten metal in a rotary motion which prevents the development of large inclusions, segregations or pockets of impurities in the continuous casting.
The continuously cast ingot is withdrawn from the lower end of the mold and continuous casting can be dressed, cut into length, rolled or otherwise processed into bodies of any desired shape and form.
While molds of various shapes and constructions have been provided, plate-type molds have been used to a significant extent in the continuous casting process for the production of continuous castings of square, rectangular and other polygonal profiles or cross sections.
A plate-type mold is a mode whose cavity is defined by a plurality of plates which are assembled together so that they abut or adjoin at the corners of the mold cavity. Such plate-type molds can be designed to impart a predetermined bend to the continuous casting as it is formed and in the casting direction to avoid bending stresses in the relatively thin shell of hardened steel surrounding the soft inner core of the continuous casting emerging from the mold.
The problems involved with such plate-type continuous casting molds and a solution to the specific problem of wear of the mold, are described in the aforementioned copending applications and the Luxembourg patent which are hereby incorporated by reference.
More specifically, plate-type molds have a decisive economic advantage by comparison with tubular molds. It is obvious that the economy of a continuous casting process depends at least in part on the left of the mold, i.e. the longer a given mold can be induced to last, the less the mold cost per ton of product will affect the economy of the continuous casting process.
Tubular molds, like plate molds, are subject to wear by erosion as the molten and solidifying metal moves through them. Thus it is advantageous to be able to renew the worn interior surfaces. It is also important to be able to restore both the original profile (cross section) and dimensions, i.e. the internal dimensions of the mold cavity.
This cannot practically be achieved with tubular molds except by depositing a layer upon the worn surfaces, a process which is prohibitively costly.
In the aforementioned copending applications and patent, a plate mold is described whereby wear can be compensated in a simple and economical manner. For example, the plate mold of this system can comprise four individual plates formed with recesses at their outer edges and interfilling in such a manner that, with grinding of the junction surfaces and by insertion of shims where the plates adjoin, it is possible to compensate precisely for the wear of the cavity-defining surfaces so that, with grinding of the abutment edges and insertion of the shims into the recesses, the mold cavity can be restored to its original dimensions. More specifically, the plate mold of these earlier systems is formed by four individual plates each having recesses at outer parts which interfit with the recesses and shoulders of adjoining plates so that contact edges between the mold surfaces can be adjusted to the same level by means of shims inserted into these recesses.
At the outer part the inner surfaces of two oppositely displaced plates are provided with bevels such that the mold cross section has eight angles corresponding to eight surfaces, four of which may be large while the other four merely form beveled corners of the continuous casting.
For compensating the worn interior faces so as to restore the mold cavity to its original dimensions, a thickness (a) is removed by any conventional machining process, e.g. grinding, from the plates having the bevels at their inner surfaces as well as from the contact surfaces while a thickness equal to the product of (a) and the cosine of the bevel angle is removed from the bevels. A thickness (b) is removed from the plates without the bevels and shims between the plates are reduced by a corresponding amount. The thicknesses (a) and (b) can be the same or different.
With this system, a plate mold can be refinished a number of times, always with resetting of the mold cross section to its original dimensions. The number of times for which this process can be repeated is limited only by the availability of shims in the recesses.
It has already been indicated that plate molds can be used in combination with electromagnetic inductors for generating rotary motion of the molten metal. In earlier constructions, the plate molds had to be supported by special frames for geometric and structural stability. These frames were disposed within the space surrounded by the inductor. Since they were composed of metal they absorbed and dissipated a significant part of the magnetic energy, a portion of the input power is lost and for a given delivery of electromagnetic power to the molten metal, a correspondingly larger inductor with higher output is required.